Process for the production of malonic acid dinitrile and purification thereof

ABSTRACT

Malonic acid dinitrile is prepared by reacting acetonitrile and cyanogen chloride in the gaseous phase at temperatures from 740* to 780*C. Temperatures from 750* to 760*C. with molar ratios of 1:1 to 1:5 of cyanogen chloride to acetonitrile are preferred. The crude mixture containing malonic acid dinitrile may be purified by conversion of the principal impurities to easily separable compounds by a Diels-Alder or selective hydrogenation reaction.

Ilnite States Patent 1191 Arni et al.

PROCESS FOR THE PRODUCTION OF MALONIC ACID DINITRILE AND PURIFICATION THEREOF [75] Inventors: Urs Arni, Brig; Adriano Faucci;

August Stocker, both of Visp, all of Switzerland [73] Assignee: Lonza, Ltd., Gampel (Valais) Basel,

Switzerland [22] Filed: Apr. 26, 1971 [21] Appl. No.: 137,593

Related US. Application Data [62] Division of Ser. No. 822,724, May 7, 1969, Pat. No.

[30] Foreign Application Priority Data May 9, 1968 Switzerland 6964/68 June 18, 1968 Switzerland... 9059/68 June 24, 1968 Switzerland 9383/68 [52] US. Cl 260/465.8 R [51] Int. Cl. C07c 121/22 [58] Field of Search 260/4658, 465.2, 260/4658 R [56] References Cited UNITED STATES PATENTS 2,799,697 7/1957 Maxion 260/4652 June 26, 1973 2,809,986 10/1957 Flisik et a]. 260/4652 3,616,269 10/1971 Aelony 61 51.". 260/465.8 R x 3,417,126 12/1968 Taguchi et a1. 260/4658 R 3,541,133 11/1970 Johnson et 31...... 260/4658 R 3,206,500 9/1965 PUIS 61 al. 260/4659 3,322,814 5/1967 lappeli 260/4651 FOREIGN PATENTS OR APPLICATIONS 44/2453 1/1969 Japan 260/4658 OTHER PUBLICATIONS Holmes; Organic Reactions; Vol. 2; 1948 pages 64, 65, 74, 75.

Primary Examiner-Joseph P. Brust Attorney-Christen & Sabol [57] ABSTRACT Malonic acid dinitrile is prepared by reacting acetonitrile and cyanogen chloride in the gaseous phase at temperatures from 740 to 780C. Temperatures from 750 to 760C. with molar ratios of 1:1 to 1:5 of cyanogen chloride to acetonitrile are preferred. The crude mixture containing malonic acid dinitrile may be purified by conversion of the principal impurities to easily separable compounds by a Diels-Alder or selective hydrogenation reaction.

7 Claims, No Drawings PROCESS FOR THE PRODUCTION OF MALONIC ACID DINITRILE AND PURIFICATION THEREOF This application is a division of U.S. Pat. application Ser. No. 822,724, filed May 7, 1969 now U.S. Pat. No. 3,655,721 issued on Apr. 11, 1972.

BACKGROUND OF THE INVENTION This invention relates to a process for the production of malonic acid dinitrile from acetonitrile and cyanogen chloride in the gaseous phase and purification thereof.

PRIOR ART U. S. Pat. No. 2,553,406 discloses that malonic acid dinitrile can be obtained by reacting acetonitrile and cyanogen chloride for a period of from 5 to seconds at a temperature above 600C. and preferably at a temperature of from 650 to 700C. According to the example, the yields amount to less than 18 percent. It is also stated in this patent that the yields are reduced even further by exceeding 700C.

U. S. Pat. No. 2,606,917 explains that where high temperatures are used, the reaction is accompanied both by decomposition and by the separation of carbon and polymers. According to this patent, the disadvantages can be avoided by using an inert gas. Unfortunately, the use of an inert gas does not provide an improvement in the poor yield of malonic acid dinitrile. Example 7 teaches a yield of only 16.8 percent is obtained at a reaction temperature of 650C. for a duration of 6 seconds with a cyanogen chloride to acetonitrile to carbon dioxide molar ratio of 12327.2.

Japanese Patent Publication 16506/66 discloses the yields are improved by introducing a small quantity of chlorine as catalyst into the gaseous reaction components, i.e., acetonitrile and cyanogen chloride. The yields are thereby improved to approximately 70 percent. However, the use of chlorine as a catalyst results in the formation of large quantities of fumaric acid dinitrile and maleic acid dinitrile as byproducts. This is particularly disadvantageous because maleic acid dinitrile is extremely difficult to separate from malonic acid dinitrile. In addition, the use of chlorine causes a considerable expense for apparatus.

The malonic acid dinitrile reaction product of acetonitrile and cyanogen chloride contains as contami nating by-products fumaric acid dinitrile and maleic acid dinitrile. The removal of these by-products from the reaction mixture involves considerable difficulty because of similarities in the physical constants.

DESCRIPTION OF THE INVENTION We have discovered that improved yields of malonic acid dinitrile are obtained by reacting acetonitrile and cyanogen chloride in the gaseous phase in the narrow temperature range of 740 to 780C. Contrary to prior art teachings of reduced yields at reaction temperatures above 700C. we obtain yields up to 70 percent without chlorine present in the gaseous reaction admixture at the above temperatures. Temperatures in the range of 750 to 760C. are preferred.

Operating at temperatures higher than 780 or lower than 740 results in lower yields. The increased temperatures cause decomposition which further increases contamination. Ordinarily, the process according to the invention is conducted at a molar ratio of cyanogen chloride to acetonitrile of 1:1 to 1:5 and preferably of 1:3 to 1:4.

We have also discovered that by purification of the crude mixture using a Diels-Alder reaction or selective hydrogenation, malonic acid dinitrile having a purity in the order of 99 percent or higher can be obtained.

Pipe shaped reactors, such as quartz pipes or metal pipes, are suitable for conducting the instant process. The-gaseous reactants can be fed to the reactor in a preheated state and the residence time of the reactants in the reactor is usually 1 to 15 seconds, and preferably at 8 to 11 seconds.

The reaction products are cooled immediately to temperatures of 20 to 50, preferably 25 to 30 C. after they leave the reactor. Cooling brine is a very effective coolant. The malonic acid dinitrile is then isolated from the cooled mixture.

According to one embodiment of the present invention, the fumaric acid dinitrile and the maleic acid dinitrile contaminants are separated from the malonic acid dinitrile contained in the reaction mixture by converting through a Diels-Alder reaction into the corresponding Diels-Alder addition compounds which are more easily separated from malonic acid dinitrile. I

Compounds with a conjugated double bond are used as reaction components for the Diels-Alder reaction and butadiene, isoprene, dimethylbutadiene, piperylene, anthracene, perylene, furan, sorbic acid are examples which are suitable. Preferably either butadiene or anthracene is used.

Depending on which Diels-Alder reaction components are used, the addition product will be either a solid or liquid at temperatures above the melting point of malonic acid dinitrile. If solid addition products are obtained, for example when anthracene or perylene are used, then the separation of the Diels-Alder reaction products can be conducted by simple filtration or centrifuging at temperatures above the melting point of the malonic acid dinitrile,-e.g., at temperatures of 35 to 40C. When liquid reaction products are obtained, for example when butadiene is used, then the separation can be conducted by simple distillation of the malonic acid dinitrile under vacuum.

The Diels-Alder reaction is conducted in the reaction mixture obtained from acetonitrile-cyanogen chloride reaction. Reaction temperatures of 40 to C. are I preferred and the reaction may be conducted in an autoclave if desired. However, it is advantageous to first remove any unreacted starting materials by distillation and separate other impurities present in small quantities such as, for example beta-chloropropionitrile by another distillation under vacuum at 5 to 30 mm Hg prior to the Diels-Alder reaction. This embodiment of the purification may be conducted continuously or batch by batch and the continuous reaction is effectively conducted in a tube-type reactor.

According to another embodiment of the present invention, the fumaric and maleic acid dinitriles contained in the reaction mixture are converted to succinic acid dinitrile by selective hydrogenation with the equivalent quantity of hydrogen in the presence of a hydrogenation catalyst. The malonic acid dinitrile is then easily separated by fractionated distillation.

The hydrogenation can be conducted in the reaction mixture as obtained from the reaction of acetonitrile and cyanogen chloride. However, the reaction mixture is preferably distilled under vacuum (for example at 80 to 110C. and 11 mm Hg), to separate the unreacted materials. Furthermore, it is also advantageous to dissolve the reaction mixture in an inert solvent and then conduct the hydrogenation. Examples of inert solvents, which will remain stable during the hydrogenation conditions are lower alcohols, such as methanol, ethanol, propanol, butanol; saturated hydrocarbons, such as benzine; aromatic hydrocarbons, such as benzene; ethers, such as dimethyl ether, diethyl ether, tetrahydrofuran and acetonitrile. The quantity of solvent used is not critical, and as an example, 300 to 700 g per 100 g of reaction mixture is suitable.

The selective hydrogenation can be conducted under normal pressure and at room temperature. Naturally, higher pressures can also be used up to about 80 atm., as can higher temperatures, up to about 100C.

Hydrogenation catalysts are well known. Examples of suitable catalysts include Raney nickel, Raney cobalt, copper, copper catalysts, such as copper chromite and preferably, palladium black and platinum black.

After the hydrogenation, the solvent is distilled off and malonic acid dinitrile is separated from the residue by fractionated distillation. in order to avoid decomposition of the malonic acid dinitrile, the distillation should be conducted under vacuum, for example 0.5 to l5 mm Hg.

The ability to hydrogenate the double-bonded carbon so selectively that no attack on nitrile groups occurs is totally unexpected.

EXAMPLE I A mixture of cyanogen chloride and acetonitrile having a mole ratio of 1:3.6 was introduced into a quartz tube heated to 760C. The tube had a length of 1.4 m and an inside diameter of 40 mm. Over a period of 3 hours, 750 g of acetonitrile and 312 g of cyanogen chloride were reacted. The residence time of the reactants in the tube was 9.8 seconds. The reaction products were immediately cooled with brine and the mixture contained 230 g of malonic acid dinitrile which corresponded to a yield of 68.4 percent of theoretical.

EXAMPLE H The Diels-Alder reaction was used to purify 100 g of the reaction product of Example I. The mixture contained 97 g malonic acid dinitrile, 2 g maleic acid dinitrile and l g fumaric acid dinitrile which was reacted with 7 g of anthracene in a glass reaction vessel with stirring for 2 hours at 140C. After cooling to 35C., the Diels-Alder addition compound was filtered off at this temperature. The filtrate was distilled at 12 mm Hg to produce 92 g of malonic acid dinitrile with a purity over 99 percent. The yield amounted to 95 percent of the malonic acid dinitrile in the crude mixture.

EXAMPLE H] A reaction product obtained by the reaction of acetonitrile and cyanogen chloride, according to the present invention had residual starting material (acetonitrile) removed by distillation. Subsequently, additional contaminates (especially betachloropropionitrile) were removed by vacuum (13 mm Hg) distillation. 80 g of this reaction mixture now contained 96 percent malonic acid dinitrile. The mixture was reacted in an autoclave with 4 g of butadiene and heated for hours at 100 110C. After distillation at l3 mm Hg, 74.7 g of pure malonic acid dinitrile having a purity of 99.8

percent were obtained. This corresponds to a yield of 97 percent.

EXAMPLE [V 160 g of a mixture having a malonic acid dinitrile content of 92 percent and about 8 percent fumaric acid dinitrile-maleic acid dinitrile combined was dissolved in 800 cc methanol. Hydrogenation was accomplished in the prsence of 1.6 g of palladium black at room temperature under atmospheric pressure. The quantity of hydrogen (4320 cc) required for the hydrogenation of the unsaturated nitriles was absorbed in about 5 l hours. After evaporation of the methanol, the remaining mixture was fractionated under vacuum in a short packed column. The main fraction (weight 124.3 g) overflowed at ll mm Hg between 98 99C. and consisted of malonic acid dinitrile with a purity of 99.8 percent.

During the distillation, small quantities of ammonia developed. Therefore, the main fraction was distilled once more (short cut distillation) with the addition of very small quantity of sulfuric acid. The resulting malonic acid dinitrile was colorless and free of ammonia. Purity of the final product was 99.91 percent.

We claim:

1. The process for the production and purification of malonic acid dinitrile which comprises: (a) reacting a reaction admixture comprised of acetonitrile and cyanogen chloride, in the gaseous phase, whereby an admixture of malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile results: (b) treating said resultant admixture which contains malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile by a purification procedure which involves converting said fumaric acid dinitrile and said maleic acid dinitrile by selective hydrogenation with hydrogen in the presence of a hydrogenation catalyst to succinic acid dinitrile; and (c) separating said malonic acid dinitrile from said succinic acid dinitrile by fractionation, whereby purified malonic acid dinitrile is obtained.

2. The process according to claim 1 wherein said resultant admixture after step (a) and before step (b), is immediately cooled to a temperature of 20 to 50C.

3. The process according to claim 1 wherein the said resultant admixture is dissolved in an inert solvent prior to the selective hydrogenation.

4. The process according to claim 3 wherein the inert solvent is methanol.

5. The process according to claim 1 wherein the selective hydrogenation is conducted at a pressure up to atmospheres and at a temperature of 20 to 100C.

6. The process according to claim 1 wherein the selective hydrogenation catalyst is palladium black.

7. The process for the production and purification of malonic acid dinitrile which comprises: (a) reacting a reaction admixture consisting of acetonitrile and cyanogen chloride in the gaseous phase at a'temperature between 740 and 780C, whereby an admixture of malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile results; (b) treating said resultant admixture which contains malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile by a purification procedure which involves converting said fumaric acid dinitrile and said maleic acid dinitrile by selective hydrogenation with hydrogen in the presence of a hydrogenation catalyst to succinic acid dinitrile; and (c) separating said malonic acid dinitrile from said succinic acid dinitrile by fractionation, whereby purified malonic acid dinitrile is obtained. 

2. The process according to claim 1 wherein said resultant admixture after step (a) and before step (b), is immediately cooled to a temperature of 20* to 50*C.
 3. The process according to claim 1 wherein the said resultant admixture is dissolved in an inert solvent prior to the selective hydrogenation.
 4. The process according to claim 3 wherein the inert solvent is methanol.
 5. The process according to claim 1 wherein the selective hydrogenation is conducted at a pressure up to 80 atmospheres and at a temperature of 20* to 100*C.
 6. The process according to claim 1 wherein the selective hydrogenation catalyst is palladium black.
 7. The process for the production and purification of malonic acid dinitrile which comprises: (a) reacting a reaction admixture consisting of acetonitrile and cyanogen chloride in the gaseous phase at a temperature between 740* and 780*C., whereby an admixture of malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile results; (b) treating said resultant admixture which contains malonic acid dinitrile, maleic acid dinitrile and fumaric acid dinitrile by a purification procedure which involves converting said fumaric acid dinitrile and said maleic acid dinitrile by selective hydrogenation with hydrogen in the presence of a hydrogenation catalyst to succinic acid dinitrile; and (c) separating said malonic acid dinitrile from said succinic acid dinitrile by fractionation, whereby purified malonic acid dinitrile is obtained. 